1. Field of the Invention:
This invention relates to tubesheets or similar apparatus for supporting tubes and is particularly concerned with an improved tubesheet possessing the strength necessary to support closely spaced heat exchange tubes.
2. Background of the Prior Art:
Tube bundles or coils are widely used to recover valuable heat from waste gases generated in furnaces, boilers and similar combustors by indirect heat transfer to another fluid, normally a liquid. The primary use of these tube bundles is to generate steam by transferring the heat from the waste gases to water. Heat transfer may be substantially increased by attaching fins to the external surfaces of the tubes comprising the bundle or coil, thereby increasing the surface area available for heat transfer. The majority of industrial heat recovery coils commercially available are comprised of horizontally oriented finned tubes that are supported near the ends and at intermediate points by tubesheets. These tubesheets are normally reinforced vertical plates with holes cut in them for the finned tubes to pass through. The holes in the tubesheets are normally about 0.25 inch larger in diameter than the finned tubes to allow the tubes to be easily passed through the holes when assembling the tube bundle.
Studies have indicated that tube bundles comprised of finned heat exchange tubes operate most efficiently when the tubes are spaced such that the outer edges of the fins on adjacent tubes comprising the bundle are about 0.5 inch or less apart along the line connecting the centers of the tubes. Tube bundles or coils having such small tube spacings are ordinarily not commercially available because conventional tubesheets designed to support tubes spaced so closely together are too weak. The bridge walls between laterally adjacent holes in a conventional tubesheet fabricated to obtain 0.5 inch tube spacings will be about 0.25 inch in length along the line that connects the centers of the holes. Tubesheets containing bridge walls of this length do not normally have the strength necessary to support the tubes. Thus a tube bundle constructed with conventional tubesheets to support and space finned heat exchange tubes will not be optimally efficient and heat will be lost that could otherwise be recovered if closer tube spacings were possible.